In recent years, discussion is made on next-generation wireless communication technology to purpose wireless communication with further high speed, great capacity, and the like in a wireless communication system such as a cellular phone system (cellular system). For example, a communication standard called long-term evolution (LTE) and a communication standard called LTE-Advanced (LTE-A) that is based on the wireless communication technology of LTE are proposed in 3rd Generation Partnership Project (3GPP) which is an organization for standardization.
The newest communication standard completed in 3GPP is Release 10 corresponding to LTE-A. Release 10 is a great functional extension of Release 8 and Release 9 corresponding to LTE. Currently, discussion is being actively made toward the completion of Release 11 that is a further extension of Release 10. Hereinafter, “LTE” is assumed to include other wireless communication systems that are extensions of LTE in addition to LTE and LTE-A unless otherwise specified.
A technology called coordinated multiple point (CoMP) is particularly taken into consideration in Release 11 of 3GPP. CoMP can refer to a technology for which transmission and reception regarding a wireless terminal (user equipment, UE) between a plurality of transmission points (TP) are coordinated. TPs here correspond to transmitter stations that are geographically separated and are a concept that substantially corresponds to a base station or a cell. Thus, a TP may be appropriately substituted with a base station or a cell hereinafter.
Several transmission schemes (categories) are available in CoMP. Joint transmission (JT), dynamic point selection/blanking (DPS/DPB or simply DPS), coordinated scheduling/beamforming (CS/CB), and the like are known as a transmission scheme of down CoMP. “Down” indicates a direction from a TP toward a UE (a so-called downlink), and conversely, “up” indicates a direction from a UE toward a TP (a so-called uplink).
Description of the CoMP transmission scheme will be made based on FIG. 1. FIG. 1A is a diagram illustrating the concept of JT which is one type of CoMP. JT is a transmission scheme in which a plurality of TPs simultaneously transmits (jointly transmits) the same data destined to a certain UE to increase a reception quality and a throughput of the UE. FIG. 1B is a diagram illustrating the concept of DPS which is one type of CoMP. DPS is a transmission scheme in which the same data destined to a UE is simultaneously present in a plurality of TPs, but a single TP transmits data to a UE while other TPs do not perform transmission (blanking). Accordingly, an instantaneous dynamic cell (TP) selection that follows fading variations is possible rather than a normal cell (TP) selection of LTE based on the state of a channel that is temporally averaged. FIG. 1C is a diagram illustrating the concept of CS/CB which is one type of CoMP. CS/CB is a transmission scheme in which a single TP performs transmission to a certain UE in a certain sub-frame, and coordinated scheduling and beamforming are performed between TPs to reduce interference given to other UEs governed by other TPs. In the present document, JT which is joint transmission performed by a plurality of TPs and DPS and CS/CB in which a plurality of TPs performs single transmission in coordination with each other may be collectively referred to as coordinated single transmission. In addition, JT of CoMP is called a single-point transmission (ST) when a single TP performs data transmission without coordinating with other TPs.
In ST in which a TP performs transmission to a UE governed by the TP, only a wireless signal transmitted from the TP is a desired wave for the UE. In other words, wireless signals of all of the TPs other than the TP that performs ST are interference waves to the UE in ST. Conversely, wireless signals from all of the TPs that are in a coordinating relationship therebetween in JT are desired waves for a UE. Thus, interference in the UE is reduced when compared with that in ST. In DPS and CS/CB, a wireless signal from one TP among the TPs that are in a coordinating relationship therebetween is a desired wave for a UE, but wireless signals (that become interference waves) are not transmitted from other TPs. Thus, interference in the UE may be reduced when compared with that in ST.
Therefore, any of the transmission schemes of CoMP reduces interference when compared with ST. Accordingly, using any CoMP transmission scheme obtains common effects such as an increase in reception quality and being capable of increasing transmission efficiency. Hereinafter, DPS will be dealt with, and CS/CB will not be dealt with unless otherwise specified because DPS and CS/CB have various similar points. However, it may be noted that CS/CB can also be dealt with in the same manner at places where DPS is dealt with hereinafter.